If non-protein-coding DNA isn’t junk, then just what is it doing?
Most of our DNA is transcribed into RNA. Since an organism struggling to survive would presumably not waste precious resources on making “junk,” widespread transcription suggests that non-protein-coding RNAs are functional. Indeed, we now know that many of them help to regulate gene expression. For example, some genes are needed during embryo development but must be turned off in the adult. Other genes are needed in certain tissues but would cause disease if expressed in others. Non-protein-coding RNAs play essential roles in regulating those genes.
Some pseudogenes regulate protein production by producing RNAs that protect or interfere with the RNAs transcribed from the genes they resemble. Repetitive DNA produces RNAs that help to inactivate the extra X chromosome in human females. Mammalian embryos depend on products of repetitive DNA to implant themselves in the uterus.
Non-protein-coding DNA can also perform functions that do not depend on transcription into RNAs. For example, in the eyes of nocturnal mammals, non-protein-coding DNA forms liquid-crystal lenses in certain cells to focus scarce rays of light at night.
To be sure, there is much DNA for which no specific functions have yet been identified. But new functions for non-protein-coding DNA are being reported every week. Anyone who claims that most of our genome consists of “junk DNA” is relying on a “Darwin of the gaps” argument—one that must constantly retreat as gaps in our knowledge are filled by new evidence.
If you could have lunch with Francis Collins and Richard Dawkins, what would you say to them about their use of the “junk DNA” argument?
Actually, Collins no longer relies on “junk DNA.” In 2007 he announced in an interview for Wired magazine that he had “stopped using the term.” In 2010 he wrote that “discoveries of the past decade, little known to most of the public, have completely overturned much of what used to be taught in high school biology. If you thought the DNA molecule comprised thousands of genes but far more ‘junk DNA,’ think again” (The Language of Life, pp. 5–6). Unfortunately, his followers at the BioLogos Institute (which he founded) seem to be unaware of this, because they continue to promote the myth that most of our DNA is junk. I would encourage Collins to set them right.
Unlike Collins, Dawkins seems utterly oblivious to recent developments in genomics. I would encourage him to read some of the scientific literature.
(Wells, he doesn’t need to. A toff is forever immune from facts. For the rest of us, seriously: More.)